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Geophysical Indicators of Gas Hydrate in the Northern Continental Margin, South China Sea  [PDF]
Xiujuan Wang,Shiguo Wu,Yiqun Guo,Shengxiong Yang,Yuehua Gong
Journal of Geological Research , 2011, DOI: 10.1155/2011/359597
Abstract: Gas hydrate drilling results show that gas hydrate has a close relationship with strong bottom-simulating reflectors (BSRs) identified from seismic data in the Baiyun sag, South China Sea. The BSRs observed on seismic profiles at the crests of submarine canyons indicate the likely existence of gas hydrate. We calculate the acoustic impedance using constrained sparse spike inversion (CSSI), the interval velocity, and the seismic reflection characteristics such as reflection strength, instantaneous frequency, blanking, and enhanced reflection to demonstrate the presence of gas hydrate. Higher acoustic impedance and P-wave velocity were identified above the BSR. A remarkable low impedance, low frequency, and acoustic blanking indicated the presence of gas below gas hydrate stability zone. The occurrence of gas hydrate at the crests of canyons suggests that the abundance of gas hydrate in Baiyun sag may be due to the migrating submarine canyons providing the structural reliefs and the topographic ridges. 1. Introduction Gas hydrates are ice-like crystalline solids and are composed of water molecules and hydrocarbon gas (usually methane). They are distributed worldwide in the continental margin sediments and beneath permafrost [1, 2]. Bottom simulating reflectors (BSRs) identified from seismic reflection profiles are conventionally interpreted as indicators for gas hydrate beneath seafloor [3]. Gas hydrates-associated BSRs have been recognized from the seismic data of other geophysical studies, and their presences have been validated by drilling or coring either in accretionary wedges [4–7] or in the continental margin of the world [8–11]. The Hikurangi Margin, east of New Zealand’s North Island, is a large marine gas hydrate province. The BSRs were identified on the multichannel seismic data and there is a strong correlation between BSR strength and geological features indicating the fluid migration [12, 13]. Geophysical parameters show that gas hydrate-bearing sediments have high elastic impedance, high P-impedance, and high P-wave velocity; and the sediments containing free gas have low elastic impedance, low P-impedance, and low P-wave velocity [14]. The anomalous velocity and the variation in amplitude and polarity of reflectors at the base of gas hydrate-bearing stability zone were used to indicate the presence of gas hydrate [15, 16]. The acoustic impedance inversion of seismic data, log to seismic correlation, and seismic attribute analyses were combined to delineate gas hydrate zone [17]. In China, eight sites were drilled in 2007 in Shenhu area,
Application of Geoid Anomalies to the Tectonic Research in the East Asian Continental Margin Application of Geoid Anomalies to the Tectonic Research in the East Asian Continental Margin  [PDF]
WU Xiaoyang,XING Junhui,LI Chaoyang,LIU Xinzhe,YANG Kai,CHEN Hongyan,GONG Wei
- , 2018,
Abstract: In this paper, we calculated multi-scale residual geoid anomalies with the method of geoid separation processing, according to EGM2008 ultra-high order gravity field model, remove-restore technique and Stokes integral. The East Asian continental margin was selected as the study area. The residual geoid anomalies have been calculated by programming. On the basis of residual geoid anomalies at various orders, the interlayer geoid anomalies at different depths were calculated to depict the spatial distribution characteristics of the residual geoid. Finally, we conducted a detailed geophysical interpretation for the study area according to the geoid anomalies in combination with other geophysical datasets. Four conclusions can be outlined as follows: 1) it is impracticable that geoid anomalies are used in the interpretation of the shallow objects due to the influence of the terrain; 2) the anomalies of residual geoid can reflect the intensity of small-scale mantle convection in the asthenosphere; 3) the interlayer geoid anomalies can reflect the magmatic activities associated with the mantle convection and mantle plume in different scales; 4) the study of the geoid may provide an approach for the research of the subduction zone, mantle convection and mantle plume
Methane hydrates in the Chilean continental margin
Morales G.,Esteban;
Electronic Journal of Biotechnology , 2003,
Abstract: in the coming years the worldwide energetic resources based on hydrocarbons will diminish, and methane hydrates can become an alternative source, given its huge deposits. chile does not have great amounts of energetic resources; however, during the cruise c-2901 on board the r/v conrad in 1998, seismic profiles that took place in the chilean continental margin between 35o and 45os show the presence of methane hydrates through bsr analysis. the following parameters for the hydrate layer can be assumed: thickness = 100 m, longitude e-w = 20 km, latitude n-s = 1000 km, hydrate concentration in the sediments = 10%, and 160 m3 of gas per m3 of hydrate. with these figures, the volume of estimated gas is 3.2 x 1013 m3.
Gas Hydrates Accumulations on the South Shetland Continental Margin: New Detection Possibilities  [PDF]
V. D. Solovyov,V. G. Bakhmutov,I. N. Korchagin,S. P. Levashov,N. A. Yakymchuk,D. N. Bozhezha
Journal of Geological Research , 2011, DOI: 10.1155/2011/514082
Abstract: The results of investigations in 2006–2010 for hydrocarbon and gas hydrates on the Antarctic Peninsula continental margin are given. In 2004 and 2006, the marine geoelectric researches by methods of forming a short-pulsed electromagnetic field (FSPEF) and vertical electric-resonance sounding (VERS) had been conducted in this region. The “deposit” type anomaly was mapped by FSPEF survey, and anomalous polarized layers of “hydrocarbon deposit” type were chosen by VERS sounding within this anomaly on Antarctic margin in the region of UAS “Academician Vernadsky.” Anomalous zones of “gas hydrate deposit” type were detected on the South Shetland margin due to the special technology of satellite data processing and interpretation using. These results confirm the high gas hydrates potential of the West Antarctica region. Some practical results of the experimental approbation of these original technologies for the “direct” prospecting and exploration of hydrocarbon (HC) and gas hydrates accumulations in different oil-and-gas bearing basins of Russia and Gulf of Mexico are proposed. The integration of satellite data processing and materials of FSPEF-VERS methods enable improving their efficiency for different geological and geophysical problems solving. 1. Introduction Previous studies have revealed the real possibilities of new mobile geophysical technologies using for hydrocarbon (HC) accumulations prospecting [1–6]. One of this technologies, method of forming a short-pulsed electromagnetic field (FSPEF) and vertical electric-resonance sounding (VERS), makes possible the efficient and accurate determination of a stratigraphic (geologic) model beneath a sounding site. The first publications about this technology as a whole had appeared in Russian (in 2001), in English—in 2003 [1, 2]. The basic physical principles that underlie the method of VERS probing described in English in the patent nos. 7227362, 7248052 (USA, 2007). On the basis of this patent in the United States was elaborated the power imaging (PI) geophysical prospecting method to aid in the exploration for hydrocarbons. PI technology is used to confirm the thickness and depth of expected hydrocarbon zones and provides a means for the direct detection of hydrocarbons [7]. Express technology of “direct” prospecting of the HC accumulations by geoelectric methods (FSPEF-VERS) was developed by experiments on the known oil and gas fields within the largest gas and condensate fields of Ukraine and once again showed the working capacity and economic efficiency of the FSPEF-VERS technology [1–6]. The
BASEMENT CONFIGURATION OF THE NORTHWESTERN SOUTH AMERICA - CARIBBEAN MARGIN FROM RECENT GEOPHYSICAL DATA
Cerón,John F.; Kellogg,James N.; Ojeda,Germán Y.;
CT&F - Ciencia, Tecnología y Futuro , 2007,
Abstract: the oceanic nature of the crust in northern colombia (underlying the lower magdalena basins) has been postulated by different authors as a northern extension of the cretaceous, mafic and ultramafic rocks accreted to the western margin of northwest colombia (in the western cordillera and baudo range). localized, small outcrops of oceanic affinity rocks seem to support this hypothesis. however, geophysical data do not support this northern extension, but clearly mark the boundary between the collisional panamá terrane with northern south america and the over thrusting of the latter on top of the obliquely convergent caribbean plate. we produced maps to basement and moho topography by integrated modeling of gravity, magnetics, seismic reflection surveys and well data from northwest colombia and the southwestern caribbean. in areas with good seismic coverage, the basement under the lower magdalena basins (lmb) is represented by a clear reflector. in areas where seismic data shows poor imaging or is absent, we use a back stripping methodology to model first the sedimentary section, with known densities, composition and geometry controlled by oil wells and high quality seismic data, and then the deeper section. 2,5d gravity and magnetics modeling results in an initial moho that can be extended to the entire region based on the control of available seismic refraction points. this controlled moho provides the basis for basement modeling for the whole area and this sequence is iterated for several sections across the region. our results indicate that the crust under northern colombia is continental to thinned continental (transitional) in nature, with densities between 2,6 and 2,7 g/cm3. our model also requires a dense wedge of sediments (density 2,5 g/cm3) at the base of the modern fold belt, which may represent a fossil sedimentary wedge attached to the continental margin. this wedge may have served as a backstop for the modern fold belt. the gravity modeling does not requ
The deep thermal characteristic of continental margin of the northern South China Sea
Jian Zhang,Jiyang Wang
Chinese Science Bulletin , 2000, DOI: 10.1007/BF02898994
Abstract: Heat flow plays an important role in the study of thermal structure and thermal evolution of continental margin of the northern South China Sea. The analysis of heat flow value shows that margin heat flow in the northern South China Sea is relatively high setting, but the percentage of crustal heat flow is lower than 35% in terrestrial heat flow. The terrestrial heat flow exhibited a current of rise from the Northern Continental Margin to the Southern Central Basin. However, the proportion of crustal heat flow in terrestrial heat flow slowly dropped down in the same direction. It is suggested that the main factor causing high heat flow setting is the moving up of hot material from asthenosphere.
Evidence of a dense water vein along the Libyan continental margin
G. P. Gasparini, A. Bonanno, S. Zgozi, G. Basilone, M. Borghini, G. Buscaino, A. Cuttitta, N. Essarbout, S. Mazzola, B. Patti, A. B. Ramadan, K. Schroeder, T. Bahri,F. Massa
Annales Geophysicae (ANGEO) , 2008,
Abstract: For the first time it was possible to investigate a still poorly known region of the eastern Mediterranean Sea, the Libyan continental margin. An oceanographic cruise, performed during summer 2006, revealed an important and novel feature: a dense vein flowing along the continental slope. The paper describes the vein evolution with some insights on its dynamic and furnishes an estimate of its transport, which results to be comparable with the Adriatic Deep Water production rate. The cascading into a steep canyon which incises the continental shelf suggests that the vein may play an important role in ventilating the deep layers of the Ionian Sea.
Sources and transport of dissolved iron and manganese along the continental margin of the Bay of Biscay
A. La s, S. Blain, P. Laan, S. J. Ussher, E. P. Achterberg, P. Tréguer,H. J. W. de Baar
Biogeosciences (BG) & Discussions (BGD) , 2007,
Abstract: Dissolved iron (DFe; <0.2 μm) and dissolved manganese (DMn; <0.2 μm) concentrations were determined in the water column of the Bay of Biscay (eastern North Atlantic Ocean) in March 2002. The samples were collected along a transect traversing from the European continental shelf over the continental slope. The highest DFe and DMn concentrations (2.39 nM and 6.10 nM, respectively) were observed in the bottom waters on the shelf at stations closest to the coast. The release of trace metal from resuspended particles and the diffusion from pore waters were probably at the origin of elevated DFe and DMn concentrations in the Bottom Boundary Layer (BBL). In the slope region, the highest total dissolvable iron (TDFe), DFe and DMn values (24.6 nM, 1.58 nM and 2.12 nM, respectively) were observed close to the bottom at depth of ca.~600–700 m. Internal wave activity and slope circulation are thought to be at the origin of this phenomenon. These processes were also very likely the cause of elevated concentrations (DFe: 1.27 nM, DMn: 2.34 nM) measured in surface waters of stations located in the same area. At stations off the continental slope, the vertical distribution of both metals were typical of open ocean conditions, indicating that inputs from the continental margin did not impact the metal distributions in the offshore waters.
Sources and transport of dissolved iron and manganese along the continental margin of the Bay of Biscay  [PDF]
A. La?s,S. Blain,P. Laan,S. J. Ussher
Biogeosciences Discussions , 2006,
Abstract: Dissolved iron (DFe; <0.2μm) and dissolved manganese (DMn; <0.2μm) concentrations were determined in the water column of the Bay of Biscay (eastern North Atlantic Ocean) in March 2002. The samples were collected along a transect traversing from the European continental shelf over the continental slope. The highest DFe and DMn concentrations (2.39 nM and 6.10 nM, respectively) were observed in the bottom waters on the shelf at stations closest to the coast. The release of trace metal from resuspended particles and the diffusion from pore waters resulted in elevated DFe and DMn concentrations in the Bottom Boundary Layer (BBL). In the slope region, the highest total dissolvable iron (TDFe), DFe and DMn values (24.6 nM, 1.58 nM and 2.12 nM, respectively) were observed close to the bottom at depth of ca. 600–700 m. Internal wave activity and slope circulation are thought to be at the origin of this phenomenon. These processes were also very likely the cause of elevated concentrations (DFe: 1.27 nM, DMn: 2.34 nM) measured in surface waters of stations located in the same area. At stations off the continental slope, the vertical distribution of both metals were typical of open ocean conditions, indicating that inputs from the continental margin did not impact the metal distributions in the offshore waters.
IODP Expedition 307 Drills Cold-Water Coral Mound Along the Irish Continental Margin
T.G. Ferdelman,Akihiro Kano,Trevor Williams,the IODP Expedition 307 Scientists
Scientific Drilling , 2006, DOI: 10.2204/iodp.sd.2.02.2006
Abstract: Introduction Over the past decade, oceanographic and geophysical surveys along the slope of the Porcupine Seabight off the southwestern continental margin of Ireland have identified upwards of a thousand enigmatic mound-like structures (Figs. 1 and 2). The mounds of the Porcupine Seabight rise from the seafl oor in water depths of 600–900 m and formimpressive conical bodies several kilometers wide and up to 200 m high. Although a few mounds such as Thérèse Mound and Galway Mound are covered by a thriving thicket of coldwater corals, most mound tops and fl anks are covered by dead coral rubble or are entirely buried by sediment (De Mol et al., 2002; Fig. 2, Beyer et al., 2003). Lophelia pertusa (Fig.3) and Madrepora oculata are the most prominent cold-water corals growing without photosynthetic symbionts. The widespread discovery of large and numerous coral-bearing banks and the association of these corals with the mounds have generated signifi cant interest as to the composition, origin and development of these mound structures.Challenger Mound, in the Belgica mound province, has an elongated shape oriented along a north-northeast to south-southwest axis and ispartially buried under Pleistocene drift sediments. In high-resolution seismic profiles the mounds appear to root on an erosion surface (van Rooij et al., 2003). During IODP Expedition307 the Challenger Mound in the Porcupine Seabight was drilled with the goal of unveiling the origin and depositional processes withinthese intriguing sedimentary structures. Challenger Mound, unlike its near neighbors the Thérèse and Galway mounds, has little to no livecoral coverage and, therefore, was chosen as the main target for drilling activities, so that no living ecosystem would be disturbed.
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